A ternary catalyst for preparing carbon nanotubes, a preparation method and application thereof

Abstract

The application discloses a ternary catalyst for preparing carbon nanotubes and a preparation method and application thereof, and belongs to the technical field of catalysts.The catalyst comprises a carrier and active components Ni, Fe and Pd, wherein the loading amount of Ni is 55-70% of the weight of the carrier, the molar ratio of Ni to Fe is 10:7-10:6, and the molar ratio of Ni to Pd is 10:2-10:1.In the catalyst, the second active component Fe and the third active component Pd are introduced in specific contents, a ternary alloy structure is formed, the service life of the catalyst is prolonged, and the activity of the catalyst and the selectivity of the carbon nanotubes are improved.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a ternary catalyst for preparing carbon nanotubes, its preparation method, and its application. Background Technology

[0002] Carbon nanotubes are one-dimensional quantum materials with a unique structure. Their radial dimensions are on the order of nanometers, and their axial dimensions are on the order of micrometers. Both ends of the tubes are essentially sealed. Due to their unique mechanical, electrical, and chemical properties, as well as their unique quasi-one-dimensional tubular molecular structure, carbon nanotubes have shown great potential application value in many fields such as microelectronics, energy, defense, and aerospace, and have become a research frontier and hot topic in the field of new materials internationally.

[0003] Currently, the main methods for preparing carbon nanotubes include: arc discharge method, chemical vapor deposition (CVD), and laser ablation method. Among them, CVD, also known as hydrocarbon gas pyrolysis, has the advantages of simple equipment, easy operation, and high efficiency in preparing carbon nanotubes, making it an ideal method for large-scale production of carbon nanotubes. Catalysts are the core technology of hydrocarbon gas pyrolysis, and nickel-based catalysts are the main catalysts used in this method to prepare carbon nanotubes.

[0004] Although existing nickel-based catalysts exhibit excellent performance, they suffer from activity degradation, severely impacting their lifespan. One major factor contributing to this activity degradation is catalyst carbon deposition. The mechanism can be described as the carbon formation rate on the active metal-gas phase side exceeding the diffusion and dissolution rate on the active metal-support side, leading to extensive carbon deposition covering the active sites. Another major factor is the agglomeration of Ni metal particles at the catalyst's active sites due to excessively high reaction temperatures. To improve lifespan and reduce catalyst deactivation at reaction temperatures, various metals and metal oxides have been introduced into Ni-based catalysts. For example, Chinese patent CN100358802C discloses a Ni / Re / Cu catalyst for preparing carbon nanotubes by contacting methane or acetylene at a suitable temperature. However, this catalyst is costly to prepare and unsuitable for large-scale carbon nanotube production. Chinese patent CN100368080C discloses a method for preparing carbon nanotubes using Ni / Al catalyst chemical vapor deposition, but the yield of carbon nanotubes prepared by this catalyst needs further improvement. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a ternary catalyst for the preparation of carbon nanotubes, wherein a specific amount of a second active component Fe and a third active component Pd are introduced into the catalyst, thereby extending the catalyst's lifespan and improving its activity.

[0006] To achieve the above objectives, according to one aspect of the present invention, a ternary catalyst for preparing carbon nanotubes is provided, the catalyst comprising a support and active components Ni, Fe and Pd, wherein the loading of Ni is 55-70% of the weight of the support, the molar ratio of Ni to Fe is 10:7-10:6, and the molar ratio of Ni to Pd is 10:2-10:1.

[0007] In some embodiments, the support is at least one of Al2O3, SiO2, MCM-41, and porous carbon materials.

[0008] In some embodiments, the catalyst has a particle size of 12-20 nm and a specific surface area of ​​260-320 m². 2 / g.

[0009] According to another aspect of the present invention, a method for preparing a ternary catalyst for preparing carbon nanotubes as described above is also provided, comprising the following steps:

[0010] (1) Weigh the soluble Ni salt, soluble Fe salt and soluble Pd salt respectively and dissolve them in deionized water. Heat in a water bath to prepare a mixed salt solution.

[0011] (2) The mixed salt solution and the carrier are impregnated in equal volumes, dried, and calcined to obtain the ternary catalyst.

[0012] In some embodiments, in step (1), the soluble Ni salt includes one or more of nickel nitrate, nickel oxalate, and nickel acetate; the soluble Fe salt includes one or more of ferric nitrate, ferric oxalate, and ferric acetate; and the soluble Pd salt is palladium nitrate.

[0013] In some embodiments, in step (1), the molar ratio of nickel ions to iron ions in the mixed salt aqueous solution is 10:7-10:6, and the molar ratio of nickel ions to palladium ions is 10:2-10:1.

[0014] In some embodiments, in step (2), the drying temperature is 100-120℃ and the drying time is 12-24h.

[0015] In some embodiments, in step (2), the calcination conditions are as follows: the temperature is increased to 650-750°C at a rate of 4-10°C / min, and calcined for 3-6 hours.

[0016] According to another aspect of the present invention, the present invention also provides the application of the above-described ternary catalyst or the ternary catalyst prepared by the above-described preparation method in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons.

[0017] In some embodiments, after the ternary catalyst is reduced, carbon nanotubes are grown at 700-850°C for 3-6 hours in a low-carbon hydrocarbon atmosphere, and then purged with N2 for 1-3 hours to obtain carbon nanotubes.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] (1) The catalyst of the present invention introduces a second active component Fe with higher carbon dissolution efficiency and a third active component Pd with even higher carbon dissolution efficiency. Pd can form a bridge for carbon transfer between metal Fe and Ni, which is beneficial to carbon transfer and reduces the carbon coverage on the Ni metal surface. It constructs a ternary alloy structure that maintains carbon balance and can limit Ni grain agglomeration, promotes the diffusion and dissolution rate of carbon on the metal-support side, effectively maintains the carbon balance on both sides of the metal, thereby reducing carbon deposition on the catalyst surface and improving the catalyst's service life. In addition, the formed ternary alloy structure effectively limits the agglomeration between Ni grains and improves the catalyst's activity.

[0020] (2) In the process of preparing carbon nanotubes using the catalyst described in this invention, due to the introduction of specific Fe and Pd into the catalyst, a “Fe-Pd carbon filter” is constructed on the surface of the metal Ni-gas phase side. Carbon preferentially passes through the “Fe-Pd carbon filter”, which makes the formed carbon nanotubes have a specific branch structure and a higher degree of graphitization, thus improving the morphology of the carbon nanotubes. Attached Figure Description

[0021] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0022] Figure 1 The images show the XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1-4 of this invention.

[0023] Figure 2 (a) and (b) are TEM images of the carbon nanotubes prepared in Example 1 and Comparative Example 6, respectively. Detailed Implementation

[0024] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0025] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0026] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0027] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0028] This invention provides a ternary catalyst for preparing carbon nanotubes, the catalyst comprising a support and active components Ni, Fe and Pd.

[0029] In some embodiments, the Ni loading in the catalyst is 55-70% of the support weight. The loading used in this invention can ensure the catalytic activity of the catalyst and provide sufficient support phase for the active metal particles, thereby improving the strength of the catalyst.

[0030] In some embodiments, the molar ratio of Ni to Fe in the catalyst is 10:7-10:6.

[0031] In some embodiments, the molar ratio of Ni to Pd in ​​the catalyst is 10:2 to 10:1.

[0032] This invention controls the molar ratios of Ni and Fe, and Ni and Pd in ​​the catalyst. This ensures that Pd can form a certain amount of bridges for carbon transfer between Fe and Ni, which is beneficial for carbon transfer, reduces the carbon coverage on the Ni metal surface, limits Ni grain agglomeration, extends the catalyst's lifespan, and improves catalytic activity. Simultaneously, by introducing specific amounts of Fe and Pd into the catalyst, a "Fe-Pd carbon filter" is constructed on the Ni-gas phase side surface. Carbon preferentially passes through this filter, resulting in carbon nanotubes with specific branching structures and a higher degree of graphitization, thus improving the morphology of the carbon nanotubes.

[0033] In some embodiments, the support is at least one of Al2O3, SiO2, MCM-41, and porous carbon materials. These supports have good structural stability, high specific surface area, and good dispersion of active centers.

[0034] In some embodiments, the particle size of the support is 2-10 nm. The support used in this application has a relatively uniform particle size, high particle size uniformity, and regular shape, thereby ensuring the uniformity of the catalyst particle size.

[0035] In some embodiments, the catalyst has a particle size of 12-20 nm and a specific surface area of ​​260-320 m². 2 / g. The catalyst of this application has a relatively uniform particle size and a large specific surface area, which is beneficial to improving the growth stability and yield of carbon nanotubes.

[0036] The present invention also provides a method for preparing the ternary catalyst for preparing carbon nanotubes as described above, comprising the following steps:

[0037] (1) Weigh the soluble Ni salt, soluble Fe salt and soluble Pd salt respectively and dissolve them in deionized water. Heat in a water bath to prepare a mixed salt solution.

[0038] (2) The mixed salt solution and the carrier are impregnated in equal volumes, dried, and calcined to obtain the ternary catalyst.

[0039] In some embodiments, in step (1), the soluble Ni salt includes one or more of nickel nitrate, nickel oxalate, and nickel acetate; the soluble Fe salt includes one or more of ferric nitrate, ferric oxalate, and ferric acetate; and the soluble Pd salt is palladium nitrate.

[0040] In some embodiments, in step (1), the molar ratio of nickel ions to iron ions in the mixed salt aqueous solution is 10:7-10:6.

[0041] In some embodiments, in step (1), the molar ratio of nickel ions to palladium ions in the mixed salt aqueous solution is 10:2-10:1.

[0042] In some embodiments, in step (1), the water bath heating temperature is 50-60℃. It is understood that the water bath heating temperature can be any specific value among 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, and 60℃, or any value within the range of 50-60℃. This invention does not specifically limit the specific method and equipment for water bath heating; commonly used water bath heating methods and equipment in the art can be adopted.

[0043] In some embodiments, in step (2), the drying temperature is 100-120℃ and the drying time is 12-24h. It is understood that the drying temperature can be any specific value among 100℃, 105℃, 110℃, 115℃, and 120℃, or any value within the range of 100-120℃; the drying time can be any specific value among 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, and 24h, or any value within the range of 12-24h.

[0044] In some embodiments, in step (2), the calcination conditions are: increasing to 650-750°C at a rate of 4-10°C / min and calcining for 3-6 hours. It is understood that the heating rate can be any specific value among 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, 6℃ / min, 6.5℃ / min, 7℃ / min, 7.5℃ / min, 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, and 10℃ / min, or any value within the range of 4-10℃ / min; the calcination temperature can be any specific value among 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, and 750℃, or any value within the range of 650-750℃; and the calcination time can be any specific value among 3h, 4h, 5h, and 6h, or any value within the range of 3-6h. This invention enables the stable bonding of metal particles by controlling the calcination conditions, resulting in a ternary alloy structure catalyst with uniform particle size and high mechanical strength. Due to the ternary alloy structure of the catalyst, it is suitable for the process of preparing carbon nanotubes by cracking low-carbon hydrocarbons, especially for high-throughput gas operations, thereby improving the yield of carbon nanotubes.

[0045] According to another aspect of the present invention, the present invention also provides the application of the above-described ternary catalyst or the ternary catalyst prepared by the above-described preparation method in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons.

[0046] In this invention, the low-carbon hydrocarbon refers to hydrocarbon gases with 1-3 carbon atoms.

[0047] In some embodiments, the low-carbon hydrocarbon includes, but is not limited to, methane, ethane, propylene, ethylene, acetylene, etc. The low-carbon hydrocarbons described in this application can rapidly decompose to produce carbon under suitable temperature conditions, providing a material basis for the subsequent efficient growth of carbon nanotubes. Preferably, the low-carbon hydrocarbon is methane.

[0048] In some specific embodiments, the method for preparing carbon nanotubes using the ternary catalyst is as follows: after reducing the ternary catalyst, carbon nanotubes are grown at 700-850°C for 3-6 hours in a low-carbon hydrocarbon atmosphere, and then purged with N2 for 1-3 hours to obtain carbon nanotubes.

[0049] In this invention, the three-way catalyst reduction treatment can be carried out using conventional reduction methods in the art, including but not limited to using hydrogen or a mixed gas for 1-2 hours. Further, the mixed gas can be 95% N2 and 5% H2 by volume. The reduction treatment can be carried out in a tube furnace.

[0050] In some embodiments, the carbon nanotube growth reaction includes: introducing low-carbon hydrocarbon gas into a reactor at a flow rate of 15-30 mL / min and reacting at a temperature of 700-850 °C for 3-6 h. Under these reaction conditions, the active metal in the ternary alloy catalyst melts upon heating; simultaneously, the low-carbon hydrocarbon gas decomposes upon heating to produce carbon. The carbon preferentially passes through the "Fe-Pd carbon filter" on the Ni-gas phase side surface of the catalyst. Since the mechanisms of carbon nanotube formation by Fe and Ni are different, the carbon nanotubes formed by Fe can act as branches forming on the back side of Ni, thus forming carbon nanotubes with a specific branched structure.

[0051] In some embodiments, after the carbon nanotube growth reaction, the tubes are purged with N2 for 1-3 hours. The purpose is to increase the graphitization degree of the carbon nanotubes and improve their morphology.

[0052] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention by way of example, and are not intended to limit the present invention.

[0053] Unless otherwise specified, all raw materials used in the embodiments and comparative examples of this invention are common commercially available products or can be prepared using conventional methods in the art. Specific information is as follows:

[0054] Carrier MCM-41: Water absorption rate 2-2.5g / g (water / carrier), particle size 2-10nm, manufacturer: Shanghai Juna Technology Co., Ltd.

[0055] Carrier SiO2: water absorption rate 2-2.5g / g (water / carrier), particle size 200-300 mesh, manufacturer: Sinopharm Chemical Reagent Co., Ltd.

[0056] Pd(NO3)2·2H2O was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., while Ni(NO3)2·6H2O and Fe(NO3)3·9H2O were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0057] Example 1

[0058] Take 60g of Ni(NO3)2·6H2O, 54g of Fe(NO3)3·9H2O and 10g of Pd(NO3)2·2H2O respectively, add 45g of deionized water, heat in a water bath to 60℃ to dissolve and prepare a mixed salt aqueous solution; impregnate an equal volume of the above mixed salt aqueous solution onto 20g of support MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The resulting catalyst is named Cat-1.

[0059] 3g of the catalyst Cat-1 was reduced with hydrogen at 750°C for 2 hours in a tube furnace, followed by the introduction of methane gas and the reaction at 750°C for 3 hours. Finally, the mixture was purged with N2 at 750°C for 1 hour to prepare the product carbon nanotubes.

[0060] Example 2

[0061] Take 60g of Ni(NO3)2·6H2O, 54g of Fe(NO3)3·9H2O and 10g of Pd(NO3)2·2H2O respectively, add 45g of deionized water, heat in a water bath to 60℃ to dissolve and prepare a mixed salt aqueous solution; impregnate an equal volume of the above mixed salt aqueous solution onto 20g of support MCM-41, dry at 120℃ for 24h, calcine at 650℃ for 5h, and maintain the heating rate at 10℃ / min. The resulting catalyst is named Cat-2.

[0062] 3g of catalyst Cat-2 was reduced in a tube furnace at 750℃ for 2h in a mixed gas (95% N2 and 5% H2 by volume), then reacted at 750℃ for 3h, and finally purged with N2 at 750℃ for 1h to prepare the product carbon nanotubes.

[0063] Example 3

[0064] Take 60g Ni(NO3)2·6H2O, 54g Fe(NO3)3·9H2O and 5.5g Pd(NO3)2·2H2O respectively, add 45g deionized water, heat in a water bath to 60℃ to dissolve and prepare a mixed salt aqueous solution; impregnate an equal volume of the above mixed salt aqueous solution onto 20g support MCM-41, dry at 120℃ for 24h, calcine at 700℃ for 5h, and maintain the heating rate at 10℃ / min. The resulting catalyst is named Cat-3.

[0065] 3g of catalyst Cat-3 was reduced with hydrogen at 750℃ for 3h in a tube furnace, then reacted at 750℃ for 3h, and finally purged with N2 at 750℃ for 1h to prepare the product carbon nanotubes.

[0066] Example 4

[0067] Take 54g Ni(NO3)2·6H2O, 42g Fe(NO3)3·9H2O and 10g Pd(NO3)2·2H2O respectively, add 45g deionized water, heat in a water bath to 60℃ to dissolve and prepare a mixed salt solution; impregnate an equal volume of the above mixed salt solution onto 20g of support MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 10℃ / min. The resulting catalyst is named Cat-4.

[0068] 3g of catalyst Cat-4 was reduced with hydrogen at 750℃ for 3h in a tube furnace, then reacted at 750℃ for 3h, and finally purged with N2 at 750℃ for 2h to prepare the product carbon nanotubes.

[0069] Example 5

[0070] Take 70g of Ni(NO3)2·6H2O, 54g of Fe(NO3)3·9H2O and 6g of Pd(NO3)2·2H2O respectively, add 45g of deionized water, heat in a water bath to 60℃ to dissolve and prepare a mixed salt aqueous solution; impregnate an equal volume of the above mixed salt aqueous solution on 20g of support SiO2, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The resulting catalyst is named Cat-5.

[0071] 3g of catalyst Cat-5 was reduced with hydrogen at 750℃ for 2h in a tube furnace, then reacted at 800℃ for 3h, and finally purged with N2 at 750℃ for 2h to prepare the product carbon nanotubes.

[0072] Comparative Example 1

[0073] The preparation method of the catalyst described in this comparative example differs from that in Example 1 in that Pd is not introduced. The specific preparation method is as follows:

[0074] Take 60g of Ni(NO3)2·6H2O and 54g of Fe(NO3)3·9H2O respectively, add 47g of deionized water, heat in a water bath to 60℃ to dissolve and prepare a mixed solution. Impregnate an equal volume of the above solution onto 20g of support MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The resulting catalyst is named D-Cat-1.

[0075] 3g of catalyst D-Cat-1 was reduced with hydrogen at 750℃ for 2h in a tube furnace, then reacted at 750℃ for 3h, and finally purged with N2 at 750℃ for 1h to prepare the product carbon nanotubes.

[0076] Comparative Example 2

[0077] The preparation method of the catalyst described in this comparative example differs from that in Example 1 in that Fe is not introduced. The specific preparation method is as follows:

[0078] Take 60g of Ni(NO3)2·6H2O and 10g of Pd(NO3)2·2H2O respectively, add 68g of deionized water, heat in a water bath to 60℃ to dissolve and prepare a mixed salt aqueous solution. Impregnate an equal volume of the above mixed salt aqueous solution onto 20g of support MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The resulting catalyst is named D-Cat-2.

[0079] 3g of catalyst D-Cat-2 was reduced with hydrogen at 750℃ for 2h in a tube furnace, then reacted at 750℃ for 3h, and finally purged with N2 at 750℃ for 1h to prepare the product carbon nanotubes.

[0080] Comparative Example 3

[0081] The preparation method of the catalyst described in this comparative example differs from that in Example 1 in that Ni is not introduced. The specific preparation method is as follows:

[0082] Take 54g of Fe(NO3)3·9H2O and 10g of Pd(NO3)2·2H2O respectively, add 65g of deionized water, heat in a water bath to 60℃ to dissolve and prepare a mixed salt aqueous solution; impregnate an equal volume of the above mixed salt aqueous solution onto 20g of support MCM-41, dry at 120℃ for 24h, calcine at 750℃ for 5h, and maintain the heating rate at 4℃ / min. The resulting catalyst is named D-Cat-3.

[0083] 3g of catalyst D-Cat-3 was reduced with hydrogen at 750℃ for 2h in a tube furnace, then reacted at 750℃ for 3h, and finally purged with N2 at 750℃ for 1h to prepare the product carbon nanotubes.

[0084] Comparative Example 4

[0085] The preparation method of the three-way catalyst described in this comparative example is the same as that in Example 1, except that the calcination conditions of the catalyst are: calcination at 450℃ for 5h, with a heating rate maintained at 4℃ / min, and the resulting catalyst is named D-Cat-4.

[0086] 3g of catalyst D-Cat-4 was reduced with hydrogen at 750℃ for 2h in a tube furnace, then reacted at 750℃ for 3h, and finally purged with N2 at 750℃ for 1h to prepare the product carbon nanotubes.

[0087] Comparative Example 5

[0088] The preparation method of the ternary catalyst described in this comparative example is the same as that in Example 1, except that 60g of Ni(NO3)2·6H2O, 22g of Fe(NO3)3·9H2O, and 2g of Pd(NO3)2·2H2O were respectively added to 45g of deionized water and heated in a water bath to 60°C to dissolve and prepare a mixed salt aqueous solution. The resulting catalyst was named D-Cat-5.

[0089] 3g of catalyst D-Cat-5 was reduced with hydrogen at 750℃ for 2h in a tube furnace, followed by the introduction of methane gas and reaction at 750℃ for 3h. Finally, N2 was used to purge at 750℃ for 1h to prepare the product carbon nanotubes.

[0090] Comparative Example 6

[0091] The preparation method of the ternary catalyst described in this comparative example is the same as that in Example 1, except that 60g of Ni(NO3)2·6H2O, 69g of Fe(NO3)3·9H2O, and 10g of Pd(NO3)2·2H2O are respectively added to 45g of deionized water and heated in a water bath to 60°C to dissolve and prepare a mixed salt aqueous solution. The resulting catalyst is named D-Cat-6.

[0092] 3g of catalyst D-Cat-6 was reduced with hydrogen at 750℃ for 2h in a tube furnace, followed by the introduction of methane gas and reaction at 750℃ for 3h. Finally, N2 was used to purge at 750℃ for 1h to prepare the product carbon nanotubes.

[0093] Performance testing

[0094] The catalysts prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to performance tests according to the corresponding test methods. The specific test methods are as follows:

[0095] The contents of Ni, Fe, and Pd in ​​the catalyst were analyzed by loading using a ZSXPrimus II X-ray fluorescence spectrometer (XRF).

[0096] Particle size: First, XRD characterization was performed on an X'Perts Power diffractometer using a CuKα target line (incident wavelength 1.54056 Å), with a scanning range of 0-90° and a scanning speed of 10° / min. Then, the particle size was calculated using the Scherrer formula.

[0097] Carbon nanotube yield: The mass before and after the reaction is measured using a precision balance. The yield is the mass of carbon nanotubes generated per unit time for 1g of catalyst.

[0098] Catalyst specific surface area (BET): The BET was measured using a Micromeritics TriStarⅡ3020 physical adsorption instrument. First, 100 mg of the sample was degassed at 200℃ for 6 h. Then, adsorption-desorption experiments were conducted in liquid nitrogen at -196℃, and data were automatically recorded by computer. The specific surface area (BET) was calculated using the adsorption data when the pressure was between 0.05 and 0.3.

[0099] Table 1. Performance evaluation results of the catalysts in Examples 1-5 and Comparative Examples 1-6

[0100] .

[0101] As shown in Table 1, the yields of carbon nanotubes prepared using the catalysts in Examples 1-5 were significantly higher than those in Comparative Examples 1-6, indicating that the catalyst of this application has a higher carbon nanotube yield. Examples 1 and Comparative Examples 1-2 show that introducing Fe or Pd alone into a nickel-based catalyst system results in low catalytic activity and lifespan of the resulting binary catalyst. Examples 1 and Comparative Example 3 show that, even in the absence of Ni, the catalytic activity and lifespan of binary catalysts containing only Fe and Pd are also relatively low. Examples 1 and Comparative Examples 5-6 show that the molar ratios of Ni / Fe and Ni / Pd in ​​the catalyst are crucial to its catalytic activity and lifespan. Therefore, this application, by introducing specific amounts of the second active component Fe and the third active component Pd into the nickel-based catalyst, achieves a synergistic effect of Ni / Fe / Pd, thereby extending the catalyst's lifespan and improving its activity.

[0102] Figure 1 These are the XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1-4 of this invention. Figure 1 It can be seen that the catalyst prepared by the preparation method in the embodiments of this application has a ternary NiFePd alloy structure, while the catalysts obtained in Comparative Examples 1-4 do not have a ternary structure.

[0103] Figure 2 (a) is a TEM image of the carbon nanotubes prepared in Example 1. Figure 2 (b) is a TEM image of the carbon nanotubes prepared in Comparative Example 6. From Figure 2 (a) and (b) show that the carbon nanotubes prepared using the catalyst prepared in Example 1 of this application have a specific branched structure and a higher degree of graphitization, and the morphology of the carbon nanotubes is improved, indicating that the molar ratio of metal elements in the ternary catalyst is very important.

[0104] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. The application of a ternary catalyst in the preparation of carbon nanotubes from low-carbon hydrocarbon cracking, characterized in that, The ternary catalyst comprises a support and active components Ni, Fe and Pd, wherein the loading of Ni is 55-65% of the weight of the support, the molar ratio of Ni to Fe is 10:7-10:6, and the molar ratio of Ni to Pd is 10:2-10:

1. The preparation method of the three-way catalyst includes the following steps: (1) Weigh the soluble Ni salt, soluble Fe salt and soluble Pd salt respectively and dissolve them in deionized water. Heat in a water bath to prepare a mixed salt solution. (2) Impregnate the mixed salt solution and the carrier in equal volumes, dry, and calcine to obtain the ternary catalyst; In step (2), the calcination conditions are: increase to 650-750℃ at a rate of 4-10℃ / min and calcin for 3-6 hours.

2. The application of the ternary catalyst according to claim 1 in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons, characterized in that, The support is at least one of Al2O3, SiO2, MCM-41, and porous carbon materials.

3. The application of the ternary catalyst according to claim 1 in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons, characterized in that, The ternary catalyst has a particle size of 12-20 nm and a specific surface area of ​​260-320 m². 2 / g.

4. The application of the ternary catalyst according to claim 1 in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons, characterized in that, In step (1), the soluble Ni salt includes one or more of nickel nitrate, nickel oxalate, and nickel acetate; the soluble Fe salt includes one or more of ferric nitrate, ferric oxalate, and ferric acetate; and the soluble Pd salt is palladium nitrate.

5. The application of the ternary catalyst according to claim 1 in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons, characterized in that, In step (2), the drying temperature is 100-120℃ and the drying time is 12-24h.

6. The application of the ternary catalyst according to claim 1 in the preparation of carbon nanotubes by cracking low-carbon hydrocarbons, characterized in that, After reducing the ternary catalyst, carbon nanotubes were grown at 700-850℃ for 3-6 hours in a low-carbon hydrocarbon atmosphere, and then purged with N2 for 1-3 hours to obtain carbon nanotubes.

Images